Liquid Oxygen-Propylene Rocket Injector

ABSTRACT

Provided herein are various improvements to rocket engine components and rocket engine operational techniques. In one example, a rocket engine propellant injection apparatus is provided that includes a manifold formed into a single body by an additive manufacturing process and comprising a fuel cavity and an oxidizer cavity. The manifold also includes one or more propellant feed stubs, the one or more propellant feed stubs protruding from the manifold and formed into the single body of the manifold by the additive manufacturing process, with at least a first stub configured to carry fuel to the fuel cavity and at least a second stub configured to carry oxidizer to the oxidizer cavity. The manifold also includes a plurality of injection features formed by apertures in a face of the manifold, ones of the plurality of injection features configured to inject the fuel and the oxidizer for combustion.

RELATED APPLICATIONS

This application is a continuation of, and claims priority to, U.S.patent application Ser. No. 15/285,324, entitled “ENHANCED LIQUIDOXYGEN-PROPYLENE ROCKET ENGINE,” and filed Oct. 4, 2016. Thisapplication also hereby claims the benefit of and priority to U.S.Provisional Patent Application 62/237,126, titled “LIQUID OXYGENPROPYLENE ENGINE AND IMPROVEMENTS THEREOF,” filed Oct. 5, 2015, which ishereby incorporated by reference in its entirety.

TECHNICAL BACKGROUND

Rocket systems can employ different engines and engine types thatreflect the particular mission launch requirements as well as the typesof payloads expected. In liquid-fueled engine configurations, fuel andoxidizer types can be selected according to energy needs, specificimpulse characteristics, and other factors. However, the design andcomponents used for rocket engines can vary considerably based upon thefuel and oxidizer selections. These components can include propellanttanks, feed lines, pumps, propellant injection components, andcombustion chambers, among other components.

One example propellant configuration includes liquid oxygen(LOX)/propylene. LOX/propylene can provide potential performance greaterthan many other propellant combinations in terms of higher specificimpulse and density due in part to the carbon double bond in propylene(a.k.a. propene) and the energy release associated with oxidation.Historically, LOX/propylene has not been a popular propellant in rocketengines, somewhat due to technical challenges with this propellant mix,as well as past industry infrastructure selections of other propellantsthat include hydrogen/LOX, rocket propellant-1 (RP-1)/LOX, LOX/methane,and various solid rocket propellants or hypergolic rocket propellants.However, various difficulties arise when using liquid propellants, suchas injector erosion, chamber heat build-up, and potential for leaks incouplings and connections among the various piping and components of theengines.

OVERVIEW

Provided herein are various improvements to rocket engine components androcket engine operational techniques. In one example, a rocket enginepropellant injection apparatus is provided that includes a manifoldformed into a single body by an additive manufacturing process andcomprising a fuel cavity and an oxidizer cavity. The manifold alsoincludes one or more propellant feed stubs, the one or more propellantfeed stubs protruding from the manifold and formed into the single bodyof the manifold by the additive manufacturing process, with at least afirst stub configured to carry fuel to the fuel cavity and at least asecond stub configured to carry oxidizer to the oxidizer cavity. Themanifold also includes a plurality of injection features formed byapertures in a face of the manifold, ones of the plurality of injectionfeatures configured to inject the fuel and the oxidizer for combustion.

This Overview is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. It may be understood that this Overview is not intended toidentify key features or essential features of the claimed subjectmatter, nor is it intended to be used to limit the scope of the claimedsubject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with referenceto the following drawings. While several implementations are describedin connection with these drawings, the disclosure is not limited to theimplementations disclosed herein. On the contrary, the intent is tocover all alternatives, modifications, and equivalents.

FIG. 1 illustrates a rocket engine system in an implementation.

FIG. 2A illustrates an injector manifold in an implementation.

FIG. 2B illustrates an injector manifold in an implementation.

FIG. 3 illustrates an injector manifold in a previous implementation.

FIG. 4 illustrates an injector manifold in an implementation.

FIG. 5 illustrates an injector manifold in an implementation.

FIG. 6A illustrates an injector manifold in an implementation.

FIG. 6B illustrates an injector manifold in an implementation.

FIG. 7 illustrates rocket engine systems in an implementation.

FIG. 8 illustrates a method of operating a rocket system.

DETAILED DESCRIPTION

Liquid rocket propellants can be employed in various rocket engines.These rocket engines can have propellants selected based on variousfactors, such as payload, mission profiles, or other factors. However,typical rocket engines are designed with particular propellants in mindwhich drives selection of components, materials, and other elements tosupport the selected propellants. The examples herein relate generallyto rocket engines that employ a propellant combination of liquid oxygen(LOX)/propylene. However, the various examples herein can includeimprovements for use in any suitable rocket engine that employs otherpropellants. These improvements can provide increased engine componentsurvivability and increased operational pressure range of the engines.

As mentioned above, LOX/propylene rocket engines provide improved launchvehicle liquid rocket engine performance potential over many otherpropellant types. This improved performance potential is derived in partfrom the carbon double bond in propylene molecules and increased energyrelease associated with oxidation. However, the use of propylene with acarbon double bond and increased energy release typically makes thecombustion process more sensitive to off-nominal operating conditions.This is especially true during start-up transients when the LOX andpropylene are transitioning between gaseous and liquid phases and at lowchamber pressures during steady-state operation. As a result, theinjectors typically are more sensitive to damage during start-up thanare engines using more standard hydrocarbon liquid fuels such as RP-1,ethanol, or supercritical fuels like hydrogen or methane.

Conventional LOX/propylene engines were initially developed for use withliquid propylene at ambient temperatures. This resulted with ranges ofpropellant input pressures that were initially constrained to minimizethe potential for off-nominal combustion during steady-state operation.To mitigate risk during start-up transients, the engine designsincorporated small wetted volumes downstream of the main valve(s) toreduce the start-up transient. Additionally, the high vapor pressure ofthe propylene and the cryogenic temperature of LOX during start-upcaused the initial flows into the injector assembly to be a complex anddynamic multi-phase process. Both propellants first gasify while theinjector elements cool down and manifold and chamber pressures rise.During this transient period, critical parameters such as combustiontemperature, injector face cooling, and chamber film cooling flow ratesare more sensitive to exceeding acceptable operating ranges if boundaryconditions are off-nominal due in part of the propylene high-energycarbon double bond noted previously. Gas bubbles also generally form inthe propylene feed lines ahead of the injector main valves duringterminal count, which in turn extends the initial gas flow phase atstart up and increases the heating rates of the injector surface.

Furthermore, if the engine were to run at chamber pressures below thevapor pressure of the propylene during steady-state combustion,cavitation within the injector manifold and flow passages generallyrestrict the mass flow and inducing severe off-nominal combustionbehavior. This is relevant to applications featuring blow-down tankpressurization systems, such as launch vehicle upper stages, which cansignificantly reduce engine performance and lead to damage of the engineinjector and/or the chamber. Historically, the length of the feed linesfrom the propellant tanks for both LOX and propylene were both kept to aminimum to ensure the propellants sitting in the feed system tubes (withgreater local heat flux/vaporization) did not experience excessive localheating and gasification.

While acceptable for development testing, such feed line configurationswould not be feasible for engine assemblies that need to include thrustvector control (TVC) capabilities. As a result, these conventionalLOX/propylene engines proved to be more sensitive to start-up conditionsand prone to damage, principally due to injector melting. Constraints onlow-end chamber pressures also inhibited several candidate applications,most notably high performance nanosat launch vehicle upper stages. Thechallenges of incorporating TVC due to the minimal feed line lengthslimited also has limited launch system applications. Additionally, highenergy combustion in a LOX/propylene rocket can damage walls of thecombustion chamber when the reacting propellants come in contact withthe walls. This damage can reduce the lifespan of the engine or lead tocatastrophic failure of the engine.

The examples herein include improvements for LOX/propylene liquid rocketengines to promote engine component longevity, especially duringstart-up transients, in order to ensure high energy release inherent inpropylene combustion while expanding the operational pressure range. Thedesign modifications and improvements discussed herein can includeinjector design modifications, improvements in propellant feed lineconfigurations, and pre-conditioning techniques for densification of thepropylene and lowering of the propylene temperature. This densificationand temperature lowering can reduce a duration of the gas-to-liquidtransition during start-up and provide sufficient cooling to theinjector components before overheating. The LOX/propylene engineexamples herein also can include improved sealing mechanisms betweeninjector elements to accommodate the lower injector temperaturesresulting from densified propylene.

As a first example of an improved rocket engine, FIG. 1 is presented.FIG. 1 is a system diagram illustrating engine system 100, which is anexample LOX/propylene engine. Engine system 100 includes combustionchamber 110 fed by injector assembly 130. Engine system 100 alsoincludes propellant feed lines 126-127 that deliver propellant toassociated valves 121-122 from propellant tanks 160-161. Although notshown in FIG. 1 for clarity, the rocket engine system can also includefurther propellant tanks, ignition systems, structural elements, chassiselements, electronic control systems, and other elements to form afunctional rocket. At least two tanks are indicated in FIG. 1, namely afuel tank configured to contain liquid propylene fuel and an oxidizertank configured to contain LOX.

In operation, cryogenic propellants contained in associated fuel andoxidizer tanks are provided through associated propellant lines 126-127to main valves 121-122. LOX tank 160 is configured to store liquidoxygen in a cryogenic state prior to ignition of engine system 100, andfuel tank 161 is configured to store liquid propylene in a densifiedstate prior to the ignition of ignition of engine system 100. Mainvalves 121-122 allow transfer of the propellants to respective stubs131-132 of injector assembly 130. Injector assembly 130 then introducesthe propellants into chamber 110 for combustion and reactive exitthrough nozzle 111. An associated rocket or other flight vehicle ispropelled by the transfer of momentum between the propellant to thevehicle. However, FIG. 1 includes several features that provide forenhanced performance These include propellant bleed valves 124-125,injector assembly 130 with integral stubs 131-132, and preconditionedfuel techniques.

A plurality of sensors 140-144 and 150-153 are included, such as thepressure and temperature sensors indicated in FIG. 1. These sensorsmonitor associated characteristics and performance of the elements ofrocket system 100 and can transfer information related to the monitoredelements to a control system comprising various electronics,electromechanical elements, hydraulics, or and circuitry. The sensorscan comprise transducers, electrical sensors, electromechanical sensors,and other sensor types. Various communication electronics can beincluded in the sensors to delivery monitored data and information to anassociated control system. Although pressure and temperature sensors areshown in FIG. 1, it should be understood that further sensor types canbe employed, such as vibration sensors, acoustic sensors, opticalsensors, stress/strain sensors, and various video or audio monitoringsystems.

To control flow of propellant to injector assembly 130 and chamber 110,such as the LOX and propylene propellants, valves 121-122 are included.These valves can share a common valve control 123, or can be separatelycontrolled. In some examples, valves 121-122 are associated withpropellant pumps or pumping mechanisms. When valves 121-122 are opening,then propellant can flow from the associated propellant lines intoinjector assembly 130. Valves 121-122 and 124-125 can comprise any valvetype and material suitable for use in a rocket engine environment andfor handling cryogenic fuels, such as ball valves, butterfly valves,needle valves, or others, including combinations thereof.

Propellant bleed valves 124-125 are also included which allow anoperator to evacuate fluid, such as vaporized propellant, from thevarious associated fuel lines. Gas or vapor content can arise inpropellant lines due to warming of cryogenic fluids from theenvironment, materials of the propellant lines, or pressure differences,or other warming events and causes. This gas or vapor content can damageelements of system 100, especially during start-up events. Bleed valves124-125 are positioned at propellant inlets of engine system 100. Bleedvalves 124-125 may be manually-operated or remotely operated valvesmounted to the engine and interface just upstream of the primary seal ofthe main valves. Bleed valves 124-125 may comprise electronically,hydraulically, or pneumatically-actuated valves. Bleed valves 124-125assist in usage of preconditioned propellant to reduce or eliminate gascontent in propellant lines during start-up when the propellant flowsinto the injector. A propellant feed system that employs these bleedvalves can ensure cold propellant at the inlet to main valves 121-122,and enable longer and more complex feed systems. For example, longerpropellant lines for both fuel and oxidizer can be employed withoutincreasing the risk of damage during engine start-up while making theengine compatible with thrust vector control elements.

Both LOX and propylene propellants can be contained in the associatedpropellant tanks 160-161 at cryogenic temperatures, and cooling systems162-163 employed by system 100 can include associated insulation,chiller mechanisms, recirculation features, heat exchangers, or otherelements. Preconditioning of the propylene or LOX can include adensification processes that cools the propellants below a desiredtemperature. The fuel may comprise densified propylene which has beencooled below ambient temperature (such as below 25° C.), or subcooledbelow the propylene atmospheric boiling point (below −50° C.). Thedensified propylene may be cooled prior to transfer to combustionchamber 110 while in or recirculating through the associated fuel tank,or may be cooled prior to loading into the associated tank.

Advantageously, system 100 can provide an improved LOX/propylene-basedrocket engine that ensures high energy release with propylene combustionwhile preventing damage to the engine components due to preconditionedor densified and cooled propellants. Rocket system 100 can use adensified propylene subcooled to cryogenic temperatures with an enhancedinjector assembly 130 and associated bleed valves. These enhancedfeatures significantly reduce the vapor pressure of this fuel, therebyminimizing start-up transients and expanding the safe operating rangefor engine pressures. Example launch systems that incorporate rocketsystem 100 can include a two-stage configuration of a nanosat launchvehicle (NLV) that can provide dedicated, cost-effective launch servicesto low Earth orbit (LEO) for the emerging “cubesat” and “nanosat”platforms. Dedicated launch systems can include system 100 and thusavoid reliance as secondary payload opportunities aboard much largerlaunch systems, which place very significant constraints on schedule,achievable orbits and spacecraft design.

In FIG. 1, injector assembly 130 comprises an enhanced injector elementfor use with densified propylene and LOX propellants. As a first exampleof injector assembly 130, FIGS. 2A and 2B are provided. FIG. 2A includesan isometric view focusing on a ‘top’ of injector 200. FIG. 2B includesan isometric view focusing on a ‘side’ of injector 200. Injector 200includes injector body or manifold 210, propellant tube stubs or stems211-212, mounting features 213, injector seal feature 214 and injectionface 215. In operation, propellant is provided to associated stubs211-212 from propellant lines (such as seen in FIG. 1). Cavities withininjector manifold 210 route the propellant to associated aperturesformed into injection face 215. One or more gaskets can be included ininjector seal feature 214 to provide a sealed mating between injector200 and an associated combustion chamber or other engine elements.

Injector 200 can be formed using a manufacturing process that includesadditive manufacturing. Additive manufacturing (AM) includes variousmanufacturing processes, such as three-dimensional (3D) printingtechniques that comprise selective sintering, directed energydeposition, metal binder jetting, powder bed fusion, or othertechniques, including combinations and improvements thereof. Althoughvarious metals or other materials can be employed to manufactureinjector 200, in this example injector 200 is formed from aluminummaterial in an additive manufacturing process. Aluminum materials caninclude aluminum metal, aluminum alloys, or aluminum compounds. Variousmaterials and metal alloys might be employed other than aluminummaterials. However, aluminum has several advantages for forming injector200 and associated features. Aluminum provides improved heat transfercharacteristics and lighter weight than other metals used for injectors,such as copper, stainless steels, and related high temperature alloysincluding Inconels.

Stubs 211-212 are formed from the same material and into the same bodyelement as manifold 210 by additive manufacturing. A taper is includedat the base of each stub where the stub meets the top face of manifold210. Further features, such as the throat and gasket mating features arealso formed using additive manufacturing. Injection face 215 is alsoformed from aluminum material and can be formed using additivemanufacturing to form features of injection face 215, such as propellantapertures, from the same body as manifold 210 and stubs 211-212.

The additive manufacturing of various rocket engine components, such asinjector 200, can expand the feasible injector geometry and minimizecomponent count. Advantageously, a reduction in separate components canresult in corresponding reduction in leaks and reliance upon joints andsealing features. The seals that remain in an engine system can comprisecryogenic O-rings, such as Teflon encapsulated stainless helical springO-rings or Teflon encapsulated silicone O-rings, among others. Theseremaining seals can handle lower internal injector temperaturesresulting from densified propylene in combination with LOX. Catastrophicleaks can thus be minimized or prevented using injector 200 when subjectto extreme temperature environments of high-heat combustion andlow-temperature cryogenic propellants. Additive manufacturing can alsoprovide embedded volumes and cavities to position propellant channelswithin close proximity to high heat flux surfaces. This positioning canfunction as a coolant for the aluminum material of the injector face,thereby dissipating the combustion heat more effectively. Flow passagesof injector 200 are sized to account for the change in density of usingpreconditioned/densified propylene versus ambient temperature propylene.

As mentioned above, stubs 211 and 212 can be formed from the samematerial and body as manifold 210. To interface stubs 211 and 212 toassociated propellant lines, various mating techniques can be employed.Due in part to stubs 211 and 212 being formed from the same body asmanifold 210 with AM techniques, various error-prone and damage-inducingmethods can be prevented. FIG. 5, discussed below, includes examplecouplings for stubs 211-212.

However, previous techniques have led to problems mating fuel andoxidizer lines to injector features. For example, FIG. 3 shows injector300 made using non-AM techniques, such as conventional subtractivemachining of a metal piece. Top plate 320 and bottom plate 321 areseparately manufactured and machined and include gasket sealing features330, 331, and 332. A separate mating plate 322 is included as well tomate to a combustion chamber. These multiple independent parts lead tousage of many individual seals and a higher probability of failure.Moreover, to interface propellant lines to injector 300, threadedconnections 310-311 are employed. The process of drilling, tapping, andthreading features 312-313 can lead to foreign object debris (FOD) aswell as imprecisions related to the multiple manufacturing and machiningsteps involved. This FOD can embed into injection apertures, wettedsurfaces, and other locations which can lead to inefficiencies andfailures of the injector. Moreover, limitations with subtractivemachining or even with casting techniques lead to non-ideal placementand sizing of cavities within injector 300. Associated sidewalls alsomust be made sufficiently large to accommodate harsh machining orcasting environments.

FOD and other machining issues are avoided using the AM-formed stubs andcompression-style fittings discussed herein. Threading, tapping, ordrilling can be avoided, providing for more reliable operation ofinjector 500 than that shown in FIG. 3. The quantity and types ofinterfaces used for subtractive machining techniques typically requiremuch larger features to contain and provide strength for the threadedsurfaces and to provide the necessary surface areas for seals. Theselarge features cause the drawback of added mass along with theassociated increase cost of this extra material. Instead ofcompression-style fittings, welding can be employed to couple the stubsto further lines. However, welding can also add process variability thatis related to the specific material being used and restricts interfacecombinations between dissimilar materials. Some materials, includingaluminum alloys, are negatively affected by the welding process (e.g.loss of strength). Using welding to permanently interface to adjacentcomponents can minimize leak paths, but have negative drawbacksincluding that the joints are not readily separable which limitserviceability and flexibility.

Advantageously, the enhanced injectors discussed herein, such asinjector 200, can be provided which is formed using AM techniques andwith built-in stubs. As a further example of enhanced injectors, FIG. 4is presented which includes a side view cutout of injector 400. In FIG.4, injector body 410 is formed from aluminum using AM techniques, andincludes integral stubs 411-412. Internal features of stubs 411 and 412can be seen in FIG. 4. Channel 421 is formed within stub 411, andchannel 422 is formed within stub 412. Channel 421 feeds into chamber orcavity 423 which forms a quasi-toroidal shape around a central cavity424 which is fed by channel 422. Injection face 425 is formed into body410 which has a plurality of apertures that allow propellants withinassociated cavities 423 and 424 to flow out of injector 400. Directionalflow arrows 430 illustrate a directional flow of propellants ejectedfrom injector 400, and a further discussion of the apertures thatproduce this directional flow is included below for FIGS. 6-7. Body 410can be mounted to structural elements of a rocket system, and injectorface can employ a seal or gasket between injector face 425 and acombustion chamber. Thus, the number of seals or gaskets can beminimized in this enhanced injector due in part to the single piece/bodyof injector 400 and stubs 411-412

Turning now to a discussion on the coupling of stubs of an enhancedinjector to fuel lines, FIG. 5 is presented. FIG. 5 illustratesmetal-metal sealing features between stubs of an injector and propellantlines or other propellant feed features. Compression fitting 550 isshown in view 501 for coupling to an associated stub of injector 500.Compression fittings can employ a mechanical swaging or flaring of tubestubs 511-512 to provide metal-to-metal seals between the AM stubs andthe interfacing fluid component/fittings. Injector 500 includes similarfeatures of injector 200 and 400, such as stubs 511-512 formed using AMtechniques into a same part or piece as body 510. View 502 illustrates afurther detailed view of the compression fitting using deformation bycompression to form a seal between stub 512 and an associated connectorfor a fuel line. Integral tube stubs 511-512 can have compressionferrules and captive nuts installed which then are configured to furthermate with connectors of propellant lines. Example types of compressionfittings include flareless fittings, flared compression fittings, singleand double ferrule fittings, CPI/A-LOK fittings, and SwagelokTwo-Ferrule Tube Fittings, among other compression fittings.

Turning now to a discussion on the enhanced injection aperture or portfeatures of the injectors discussed herein, FIGS. 6A and 6B areprovided. FIG. 6A is included to show non-optimized injection aperturesin an injector 600. Metal erosion can occur around both LOX ports andpropylene ports due to placement and directionality of the associatedports. Moreover, overheating of associated combustion chambers can arisefrom the high temperatures associated with combustion.

FIG. 6B illustrates an enhanced injector aperture configuration 620. Theindividual injection apertures or ports can be associated with eitherLOX or propylene and are fed by the respective cavity or chamberillustrated in previous figures, such as cavities 423 and 424 in FIG. 4.A “split-triplet” configuration is shown in FIG. 6B, with an innerportion 624 of a single ring of ports dedicated to fuel injection, amiddle portion 623 of two-rows of ports dedicated to LOX injection, andan outer portion 622 of a single row of ports dedicated to fuelinjection. A final outer portion 621 is included to inject fuel as well.Advantageously, the configuration shown in FIG. 6B provides for minimalor no erosion of the injection plate and ports over a desired lifetimeof the injector.

Directionality features are also incorporated into each of the ports.Specifically, the portions 622, 623, and 624 are configured to injectassociated propellant (LOX and fuel) inward with respect to a centerlineof injector 620. Portion 621 is configured to inject fuel outward andtowards walls of an associated combustion chamber. The enhancedinjection scheme employed in injector 620 directs propellant flowtowards the centerline and away from the walls of the chamber. This canestablish a barrier boundary layer to form along the walls of thechamber in order to help insulate the chamber walls from the highestheat regions of combustion. Further detail on the directionality isillustrated in FIG. 7.

FIG. 7 illustrates a rocket engine system in an implementation. Aportion of a rocket engine system is shown in configuration 700 thatincludes a side view of injector 710 and a portion of chamber 715. Feedstubs 711-712 are also shown in FIG. 7 to further illustrate theirassociated features.

Configuration 700 is included to further illustrate the directionalinjection features of an enhanced injector discussed herein. Forexample, the inner portions 622, 623, and 624 of FIG. 6 can be employedto direct LOX and fuel into a center conical flow. The center conicalflow can be described as the propellant moving towards the chambercenter line. The central four rings of orifices on injector 710 (i.e.inner portions 622, 623, and 624 of injector 620) form the resultantflow 741. Configuration 701 illustrates inner rings 751 of injectionorifices or apertures which corresponds to flow 741. Individual jetsemerge from the face of injector 710 before hitting/merging with eachother and forming the conical flow. The outwardly flowing small jets 740can be formed from orifices formed around a perimeter of the injectorface (i.e. portion 621 of injector 620) form a fuel film for coolingwalls of chamber 715 by impinging on the walls of chamber 715.Configuration 701 illustrates outer ring 750 of injection orifices orapertures which corresponds to flow 740.

Configuration 702 illustrates an engine system vertically installed intotest stand 720 for experimental testing of the associated engine system721. Nozzle 722 has propellant 723 exiting for use in propulsion. Theenhanced features illustrated in configurations 700 and 701 can beemployed in configuration 702 to provide for a LOX/propylene engine witha high-energy release resultant from densified propylene combustion andthe low-temperature environments of its cryogenic propellants.

Thus, the examples in FIGS. 6 and 7 illustrate various enhanced featuresof injectors and associated orifices/ports/apertures. These injectorfeatures provided for minimized damage such as injector melting,especially during start-up transients. The injector and associatedenhanced features herein can be deployed in improved LOX/propyleneengines with injectors that are capable of withstanding the high heatenvironment of due to high energy hydrocarbon combustion. Use ofdensified propylene is also provided herein, and injectors and injectionapertures are capable of using densified propylene. Furthermore, flowpassages and apertures of injectors are sized to account for the changein density of using preconditioned/densified propylene versus ambienttemperature propylene.

Directionality of propellant injection into the chamber volume isprovided to reduce heat flux onto the chamber walls. For example, flowmomentum is angled towards a centerline of a combustion chamber toreduce heat flux from combustion onto the chamber walls. Moreover, jetsof fuel are projected onto the chamber walls to establish a film orlayer of fuel for cooling the chamber walls. The vaporization and otherprocesses associated with the fuel film projected onto the chamber wallsprovides conductive cooling due to the cryogenic temperatures of thefuel as well as evaporative cooling from the fuel interacting with theheat of combustion in the central conical propellant injection.

To further illustrate the operation of the rocket engine systems andinjection features herein, FIG. 8 is provided. FIG. 8 is a flow diagramthat illustrates a method of operating a rocket system. The rocketsystems employed to operate according to the descriptions in FIG. 8 caninclude any of the enhanced systems and elements discussed herein, suchas system 100 of FIG. 1, injector 200 of FIG. 2, injector 400 of FIG. 4,injector 500 of FIG. 5, injector 620 of FIG. 6, and the configurationsof FIG. 7, including combinations and variations thereof. However, forpurposes of clarity, the operations of FIG. 8 will be discussed in thecontext of the elements of FIG. 1.

In FIG. 8, liquid propylene fuel is preconditioned to a selecteddensification level (801). This preconditioning includes cooling thepropylene fuel using any suitable cryogenic cooling system. Both LOX andpropylene propellants can be contained in associated propellant tanks160-161 at cryogenic temperatures, and cooling systems 162-163 employedby system 100 can include associated insulation, chiller mechanisms,recirculation features, heat exchangers, or other elements.Preconditioning of the propylene (or LOX) can include a densificationprocesses that cools the propellants below a desired temperature. Thefuel may comprise densified propylene which has been cooled belowambient temperature (such as below 25° C.), or subcooled below thepropylene atmospheric boiling point (below −50° C.). The densifiedpropylene may be cooled prior to transfer to combustion chamber 110while in or recirculating through the associated fuel tank, or may becooled prior to loading into the associated tank.

System 100 provides (802) preconditioned propylene to fuel main valve122, and provides (804) liquid oxygen to LOX main valve 121. In FIG. 1,fuel line 127 and LOX line 126 provide associated propellants to mainvalves 121-122. However, vapor or gas bubbles can form in propellantlines due to contact of the propellants with materials of the propellantlines, the distances or lengths of the propellant lines, the temperatureof the environment surrounding system 100, or timeframes involved instorage of the cryogenic propellants, among other vapor-forming events.These gas bubbles or volumes of vapor can lead to damage to enginesystem 100 during startup and ignition.

During engine start-up, the high vapor pressure of the propylene and thecryogenic temperature of propellants can cause the initial flows intoinjector assembly 130 to be a complex and dynamic multi-phase process.Both propellants first gasify while the injector elements cool down andmanifold and chamber pressures rise. During this transient period,critical parameters such as combustion temperature, injector facecooling, and chamber film cooling flow rates are more sensitive toexceeding acceptable operating ranges if boundary conditions areoff-nominal, in part because of the propylene high-energy carbon doublebond noted previously. It has also been found that gas bubbles can formin the propellant feed lines ahead of the injector main valves duringterminal count, which in turn extends the initial gas flow phase atstart up and increases the heating rates of the injector surface. Inaddition, if, during steady-state combustion, the engine were to run atchamber pressures below the vapor pressure of the propylene, the latterwill cavitate (gasify) within the injector manifold and flow passages,again restricting mass flow and inducing severe off-nominal combustionbehavior. This is most relevant to applications featuring blow-down tankpressurization systems, such as launch vehicle upper stages. At aminimum, this phenomenon can significantly reduce engine performance andunder extreme conditions lead to damage of the engine injector and/orthe chamber.

To prevent damage to engine system 100, bleed valve 124 is included toevacuate vaporized propylene (803), and bleed valve 125 is used toevacuate vaporized LOX (805). Bleed valves 124-125 may bemanually-operated or remotely operated valves mounted to the engine andinterface just upstream of the primary seal of the main valves. Bleedvalves 124-125 may comprise electronically, hydraulically, orpneumatically-actuated valves. Bleed valves 124-125 assist in usage ofpreconditioned propellant to reduce or eliminate gas content inpropellant lines during start-up when the propellant flows into theinjector. Evacuation of gas content in the propellant lines can providecold propellant at the inlet to main valves 121-122, and enable longerand more complex feed systems that comprise lines 126-127. For example,longer propellant lines for both fuel and oxidizer can be employedwithout increasing the risk of damage during engine start-up whilemaking the engine compatible with thrust vector control elements.

Once the gas content in the propellant lines has been bled using bleedvalves 124-125, engine system 100 directs (806) preconditioned propyleneand lox inward through injection apertures and propylene outward throughside cooling apertures (806), and an associated ignitor then ignites thesubcooled propylene and lox to start rocket engine (807). In FIG. 1,injector assembly 130 is employed to inject propellant into chamber 110.Various apertures or orifices are provided in injector assembly 130,such as those shown in FIGS. 6B and 7, to direct the LOX and a portionof the fuel into a central conical flow indicated by directional arrows133 in FIG. 1. A second portion of fuel is directed toward walls ofchamber 110 through apertures dedicated to cooling the chamber wallswith cryogenic fuel. Thus, FIG. 1 illustrates a layered combustionprofile, with a barrier layer 112 formed from impinging cryogenic fuelonto the walls of chamber 110. Combustion zone 113 comprises a volumewhere fuel and LOX are combined and combusting, while zone 114 indicatesthe exit of combusting and combusted propellants out of nozzle 111.

Certain inventive aspects may be appreciated from the foregoingdisclosure, of which the following are various examples.

EXAMPLE 1

A rocket engine propellant injection apparatus, comprising an injectorassembly formed into single body by an additive manufacturing process.The injector assembly comprising a fuel cavity, an oxidizer cavity, andone or more propellant feed stubs protruding from the injector assemblyand formed into the single body of the injector assembly by the additivemanufacturing process, with at least a first stub configured to carryfuel to the fuel cavity and at least a second stub configured to carryoxidizer to the oxidizer cavity. The injector assembly including aplurality of injection features comprising by apertures in a face of theinjector assembly, ones of the plurality of injection featuresconfigured to inject the fuel and the oxidizer for combustion.

EXAMPLE 2

The apparatus of Example 1, comprising the injector assembly comprisingan aluminum material that forms the single body by the additivemanufacturing process.

EXAMPLE 3

The apparatus of Examples 1-2, where the rocket engine propellantinjection apparatus is configured to employ densified propylene as thefuel and liquid oxygen as the oxidizer.

EXAMPLE 4

The apparatus of Examples 1-3, comprising the one or more propellantfeed stubs forming tube structures tapered outwards from a first face ofthe injector assembly and configured to mate with compression-typefittings for attachment to associated propellant feed lines.

EXAMPLE 5

The apparatus of Examples 1-4, comprising the plurality of injectionfeatures formed into the single body by the additive manufacturingprocess.

EXAMPLE 6

The apparatus of Examples 1-5, comprising the plurality of injectionfeatures comprising a first portion of orifices configured to injectfuel and oxidizer in a generally conical shape directed inward withrespect to an associated combustion chamber wall.

EXAMPLE 7

The apparatus of Examples 1-6, comprising the plurality of injectionfeatures comprising a second portion of orifices configured to injectfuel directed outward at the associated combustion chamber wall forcooling of the associated combustion chamber wall.

EXAMPLE 8

A liquid rocket engine, comprising a combustion chamber configured toreceive liquid oxygen and liquid propylene for combustion, a firstpropellant feed line configured to carry the liquid oxygen from a firstpropellant tank to a first main valve, a second propellant feed lineconfigured to carry the liquid propylene from a second propellant tankto a second main valve, and an injector assembly configured to receivethe liquid oxygen and the liquid propylene from associated ones of thefirst and second main valves and inject the liquid oxygen and the liquidpropylene into the combustion chamber. The injector assembly formed intosingle body by an additive manufacturing process and comprising a fuelcavity, an oxidizer cavity, and one or more propellant feed stubsprotruding from the injector assembly and formed into the single body ofthe injector assembly by the additive manufacturing process, with atleast a first stub configured to carry the liquid propylene to the fuelcavity and at least a second stub configured to carry the liquid oxygento the oxidizer cavity. The injector assembly further comprising aplurality of injection features comprising by apertures in a face of theinjector assembly, ones of the plurality of injection featuresconfigured to inject the liquid oxygen and the liquid propylene into thecombustion chamber for combustion.

EXAMPLE 9

The liquid rocket engine of Example 8, comprising the injector assemblycomprising an aluminum material that forms the single body by theadditive manufacturing process.

EXAMPLE 10

The liquid rocket engine of Examples 8-9, where the liquid propylenecomprises densified propylene cooled below at least one of an ambienttemperature and an atmospheric boiling point of propylene.

EXAMPLE 11

The liquid rocket engine of Examples 8-10, comprising the one or morepropellant feed stubs forming tube structures outwards from a first faceof the injector assembly, the first face opposite a face of the injectorassembly comprising the plurality of injection features.

EXAMPLE 12

The liquid rocket engine of Examples 8-11, comprising the one or morepropellant feed stubs configured to mate with compression-type fittingsfor attachment to associated propellant feed lines routed from theassociated ones of the first and second main valves.

EXAMPLE 13

The liquid rocket engine of Examples 8-12, comprising the plurality ofinjection features formed into the single body by the additivemanufacturing process, and comprising a first portion of orificesconfigured to inject fuel and oxidizer in a generally conical shapedirected towards a centerline of the combustion chamber.

EXAMPLE 14

The liquid rocket engine of Examples 8-13, comprising the plurality ofinjection features comprising a second portion of orifices configured toinject fuel directed outward at a wall of the combustion chamber forcooling of the wall of the combustion chamber.

EXAMPLE 15

The liquid rocket engine of Examples 8-14, comprising a first bleedvalve coupled to the first propellant feed line before the first mainvalve and configured to selectively evacuate at least a portion ofvaporized liquid oxygen within the first propellant feed line, and asecond bleed valve coupled to the second propellant feed line before thesecond main valve and configured to selectively evacuate at least aportion of vaporized liquid propylene within the second propellant feedline.

EXAMPLE 16

The liquid rocket engine of Examples 8-15, comprising a first propellanttank configured to store the liquid oxygen in a cryogenic state prior toignition of the liquid rocket engine, and a second propellant tankconfigured to store the liquid propylene in a densified state prior tothe ignition of the liquid rocket engine.

EXAMPLE 17

A method of manufacturing a rocket engine propellant injectionapparatus. The method comprising forming an injector assembly intosingle body by an additive manufacturing process, where the single bodyof the injector assembly comprises a fuel cavity and an oxidizer cavity.The method includes forming at least a first propellant feed stub intothe single body by the additive manufacturing process to provide a firstchannel to carry fuel to the fuel cavity, forming at least a secondpropellant feed stub into the single body by the additive manufacturingprocess to provide a second channel to carry oxidizer to the oxidizercavity, and forming a plurality of propellant injection features intothe single body by the additive manufacturing process comprisingapertures in a face of the injector assembly.

EXAMPLE 18

The method of Example 17, further comprising forming the injectorassembly into the single body using an aluminum material in the additivemanufacturing process.

EXAMPLE 19

The method of Examples 17-18, further comprising attaching a firstcompression fitting to the first propellant feed stub and a secondcompression fitting to the second propellant feed stub, the first andsecond compression fittings configured to couple to associatedpropellant lines.

EXAMPLE 20

The method of Examples 17-19, further comprising forming the pluralityof injection features to include a first portion of directional orificesconfigured to inject fuel and oxidizer in a generally conical shapedirected towards a centerline of a combustion chamber, and a secondportion of directional orifices configured to inject fuel directedoutward at a wall of the combustion chamber.

EXAMPLE 21

A method of providing propellant to a combustion chamber of a rocketengine. The method comprising preconditioning liquid propylene into adensified state and providing densified propylene to a fuel tankassociated with the rocket engine, providing liquid oxygen to anoxidizer tank associated with the rocket engine, purging vaporizeddensified propylene from one or more fuel feed lines that provide thedensified propylene from the fuel tank to a fuel valve of the rocketengine, and purging vaporized liquid oxygen from one or more oxidizerfeed lines that provide the liquid oxygen from the oxidizer tank to anoxidizer valve of the rocket engine. The method also includes engagingthe fuel valve to provide the densified propylene to an injectorassembly, engaging the oxidizer valve to provide the liquid oxygen tothe injector assembly, injecting the densified propylene and the liquidoxygen from apertures in the injector assembly into a combustion chamberof the rocket engine, and igniting the densified propylene and theliquid oxygen within the combustion chamber to provide propulsionassociated with the rocket engine.

EXAMPLE 22

The method of Example 21, where preconditioning the liquid propylenecomprises cooling the liquid propylene below an ambient temperature.

EXAMPLE 23

The method of Examples 21-22, where preconditioning the liquid propylenecomprises sub-cooling the liquid propylene below an atmospheric boilingpoint of the liquid propylene.

EXAMPLE 24

The method of Examples 21-23, comprising purging the vaporized densifiedpropylene using one or more fuel bleed valves, and purging the vaporizedliquid oxygen using one or more oxidizer bleed valves.

EXAMPLE 25

The method of Examples 21-24, comprising injecting the liquid oxygen andat least a first portion of the densified propylene from a first portionof the apertures in the injection assembly in a generally conical shapedirected towards a centerline of the combustion chamber.

EXAMPLE 26

The method of Examples 21-25, comprising injecting at least a secondportion of the densified propylene from a second portion of theapertures in the injection assembly directed outward at a wall of thecombustion chamber for cooling of the wall of the combustion chamber.

The functional block diagrams, operational scenarios and sequences, andflow diagrams provided in the Figures are representative of exemplarysystems, environments, and methodologies for performing novel aspects ofthe disclosure. While, for purposes of simplicity of explanation,methods included herein may be in the form of a functional diagram,operational scenario or sequence, or flow diagram, and may be describedas a series of acts, it is to be understood and appreciated that themethods are not limited by the order of acts, as some acts may, inaccordance therewith, occur in a different order and/or concurrentlywith other acts from that shown and described herein. For example, thoseskilled in the art will understand and appreciate that a method couldalternatively be represented as a series of interrelated states orevents, such as in a state diagram. Moreover, not all acts illustratedin a methodology may be required for a novel implementation.

The various materials, manufacturing processes, and propellantsdiscussed herein are employed according to the descriptions above.However, it should be understood that the disclosures and enhancementsherein are not limited to these materials, manufacturing processes, andpropellants, and can be applicable across a range of suitable materials,manufacturing processes, and propellants. Thus, the descriptions andfigures included herein depict specific implementations to teach thoseskilled in the art how to make and use the best options. For the purposeof teaching inventive principles, some conventional aspects have beensimplified or omitted. Those skilled in the art will appreciatevariations from these implementations that fall within the scope of thisdisclosure. Those skilled in the art will also appreciate that thefeatures described above can be combined in various ways to formmultiple implementations.

What is claimed is:
 1. A rocket engine injector apparatus, comprising:an injector body formed by an additive manufacturing process; a fuelcavity in the injector body; an oxidizer cavity that forms a generallytoroidal shape around the fuel cavity; feed stubs formed into theinjector body by the additive manufacturing process, the feed stubscomprising tube structures projecting outwards from a first face of theinjector body and having swaged or flared features to mate withcompression-type fittings in a metal-to-metal seal for attachment toassociated feed lines; wherein at least a first feed stub extendsoutward from a first position of the first face of the injector body andis configured to carry fuel through a first channel to the fuel cavity;wherein at least a second feed stub extends outward from the first faceof the injector body in a position offset from the first position and isconfigured to carry oxidizer through a second channel to the oxidizercavity; and a plurality of injection apertures in a second face of theinjector body opposite the first face of the injector body configured toinject the fuel and the oxidizer for combustion, with each of the fuelcavity and the oxidizer cavity feeding a corresponding subset of theinjection apertures.
 2. The apparatus of claim 1, wherein flow passagesof at least the injector body are sized to account for densifiedpropylene as the fuel and liquid oxygen as the oxidizer.
 3. Theapparatus of claim 2, wherein the density of the densified propylenecorresponds to propylene cooled below approximately 25° C.
 4. Theapparatus of claim 1, comprising: the injector body comprising analuminum material that forms a single body by the additive manufacturingprocess.
 5. The apparatus of claim 1, comprising: the plurality ofinjection apertures formed into the injector body by the additivemanufacturing process.
 6. The apparatus of claim 1, comprising: theplurality of injection apertures comprising a first portion configuredto inject fuel and oxidizer in a generally conical shape directed inwardwith respect to an associated combustion chamber wall.
 7. The apparatusof claim 6, comprising: the plurality of injection apertures comprisinga second portion configured to inject fuel directed outward at theassociated combustion chamber wall for cooling of the associatedcombustion chamber wall.
 8. A rocket engine, comprising: a combustionchamber configured to receive liquid oxygen and liquid propylene; afirst feed line configured to carry the liquid oxygen from a first tankto a first main valve; a second feed line configured to carry the liquidpropylene from a second tank to a second main valve; and an injectorassembly configured to receive the liquid oxygen and the liquidpropylene from associated ones of the first and second main valves andinject the liquid oxygen and the liquid propylene into the combustionchamber, the injector assembly formed into a body by an additivemanufacturing process and comprising: a fuel cavity; an oxidizer cavitythat forms a quasi-toroidal shape around the fuel cavity; feed stubsforming tube structures tapered outwards from a first face of theinjector assembly and formed into the body of the injector assembly bythe additive manufacturing process, wherein the feed stubs are eachmechanically swaged or flared to mate with a compression-type fitting ina metal-to-metal seal for attachment to an associated feed line routedfrom the associated ones of the first and second main valves; wherein atleast a first stub extends outward from a first position of the firstface of the injector assembly and is configured to carry the liquidpropylene to the fuel cavity; wherein at least a second stub extendsoutward from the first face of the injector assembly in a positionoffset from the first position and is configured to carry the liquidoxygen to the oxidizer cavity; and injection apertures in a second faceof the injector assembly opposite the first face of the injectorassembly, each of the fuel cavity and the oxidizer cavity feeding acorresponding subset of the injection apertures, with corresponding onesof the injection apertures configured to inject the liquid oxygen andthe liquid propylene into the combustion chamber for combustion.
 9. Therocket engine of claim 8, wherein flow passages of at least the injectorassembly are sized to account for densified liquid propylene as the fueland the liquid oxygen as the oxidizer.
 10. The rocket engine of claim 9,wherein the density of the densified liquid propylene corresponds to theliquid propylene cooled below approximately 25° C.
 11. The rocket engineof claim 8, comprising: the injector assembly comprising an aluminummaterial that forms the single body by the additive manufacturingprocess.
 12. The rocket engine of claim 8, comprising: the injectionapertures formed into the single body by the additive manufacturingprocess, and comprising a first portion configured to inject fuel andoxidizer in a generally conical shape directed towards a centerline ofthe combustion chamber.
 13. The rocket engine of claim 12, comprising:the injection apertures comprising a second portion configured to injectfuel directed outward at a wall of the combustion chamber for cooling ofthe wall of the combustion chamber.
 14. The rocket engine of claim 8,comprising: a first bleed valve coupled to the first feed line beforethe first main valve and configured to selectively evacuate at least aportion of vaporized liquid oxygen within the first feed line; and asecond bleed valve coupled to the second feed line before the secondmain valve and configured to selectively evacuate at least a portion ofvaporized liquid propylene within the second feed line.
 15. The rocketengine of claim 8, comprising: a first tank configured to store theliquid oxygen in a cryogenic state prior to ignition of the liquidrocket engine; and a second tank configured to store the liquidpropylene in a densified state prior to the ignition of the liquidrocket engine.
 16. A method comprising: forming an injector assembly fora rocket engine into a body by an additive manufacturing process,wherein the body of the injector assembly comprises a fuel cavity and anoxidizer cavity that forms a generally toroidal shape around the fuelcavity; forming at least a first feed stub into a first face of the bodyand tapering outwards from a central position on the first face of thebody by the additive manufacturing process to provide a first channel tocarry fuel to the fuel cavity; forming at least a second feed stub intothe first face of the body and tapering outwards from a position offsetfrom the central position on the first face of the body by the additivemanufacturing process to provide a second channel to carry oxidizer tothe oxidizer cavity; forming propellant injection features into the bodyby the additive manufacturing process in a second face of the injectorassembly opposite the first face of the injector assembly; and attachinga first compression fitting to the first feed stub and a secondcompression fitting to the second feed stub in a metal-to-metal seal,the first and second compression fittings each mechanically swaged orflared to couple to associated propellant lines.
 17. The method of claim16, further comprising: sizing flow passages of the injector assembly toaccount for a change in density of using liquid propylene as the fueland liquid oxygen as the oxidizer.
 18. The method of claim 17, whereinthe liquid propylene comprises densified propylene cooled belowapproximately 25° C.
 19. The method of claim 16, further comprising:forming the injector assembly into the body using an aluminum materialin the additive manufacturing process.
 20. The method of claim 16,further comprising: forming the propellant injection features to includefirst orifices configured to inject fuel and oxidizer in a generallyconical shape directed towards a centerline of a combustion chamber, andsecond orifices configured to inject fuel directed outward at a wall ofthe combustion chamber.